Process of baking molded pieces



Sept. 20, 1932. E. J. HALL I .PROCESS OF BAKING MOLDED PIECES Filed July20, 1926 Patented Sept. 20, 1932 UNITED STATES PATENT OFFICE EVERETT J.HALL, OF ELIZABETH, NEW JERSEY, ASSIGNOR TO METALS DISINTEGRAT- INGCOMPANY, INC., 01 ELIZABETH, NEW JERSEY, A CORPORATION OF NEW JERSEYPROCESS OF BAKING MOLDED PIECES Application filed July 20, 1926. SerialNo. 123,699.

This invention aims to provide an improved commutator brush, andincludes a manufacturing method appropriate to the product.

An object is the production of an improved commutator brush having adurable pigtail attached thereto in a manner to provide a permanent andperfect contact between brush and pigtail. The invention also involvesan expeditious and economical method of producing the brushes, importantsaving of time, labor, material and fuel being accomplished thereby.

While I have disclosed a preferred form of the invention, it should beunderstood that various changes may be made without departing from thespirit and scope of the invention as hereinafter set forth and claimed.

In the drawing Fig. 1 shows the processof molding the brush in the pillmachine Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3 is a section on line 3-3 of Fig. 1;

Fig. 4 is a perspective of the bottom die;

Fig. 5 is a perspective of the completed brush.

Brushes of the type herein disclosed are ordinarily formed bycompressing powdere' material in a pill machine of well-knownconstruction. The usual practice is to mold the brush blank on the flat,so that the laminations will run perpendicular to the commutator and inline with the bars. These blanks, after molding, are packed in suitablecon-' tainers (a couple of thousand at a time), surrounded either withsand or a sand containing some carbonaceous material, the function ofthe sand being to separate the brushes and prevent their stickingtogether during the ensuing baking operation. The containers are thenplaced in a furnace and fired at a temperature of 650 to 7 (3., and inorder for complete heat penetration and uniform baking conditions a24-hour cycle is usually required. After baking, the brush blanks areseparated from the sand and then drilled to permit the introduction ofpigtail wires, usually braided wires; the wire connection cleaned, ortreated in some way with mercury to insure good intermetallic contact;and the brush then introduced into a forming die, which presses thebrush onto the pigtail wire, giving a good contact and the same timecompressing the brush to SlZe.

As these brushes are molded'on the flat, and as it has to date beendifiicult, if not impossible, to maintain the thickness of the brushwithin the limits required for a proper fit in the motor brush-holder,it has been necessary to size the brushes, which is done either bygrinding, in some instances, or by forcing them to size with a properdie, during the pigtailing operation. Moderate variations in the lengthof the brush are of no importance whatsoever, as these are taken care ofby the spring feed.

The present invention aims to effect economies in the cost ofmanufacture and at the same time produce a much better pigtail andpigtail connection, by molding the brush around the pigtail wire, and bya novel subsequent treatment.

As shown in Fig. 1 the mold, which may be part of a so-called pillmachine, comprises a rectangular sleeve 10 having an openingtherethrough of a size corresponding to the J thickness and width of thefinished brush.

The bottom die 11 is formed with an indented top and channeled sides asshown in Figs. 2 and 4:. 1 A piece of pigtail wire 12, which may be ofordinary copper, deoxidized copper, or other suitable material, andpreferablyv braided, is placed over the bottom die, fitting into thechannels, and supported above the bottom of the indentation formed inthe top of the die block. The die block is placed in Sleeve 10, which isthen filled with the proper amount of powder (a mixture of powderedcopper, lead and graphite, for instance) and the plunger 13 is broughtdown to compress the powder. This action presses the powder under andentirely around the portion of Wire 12 lying above the lower die block,and forces the powder into the interstices and surface irregularities ofthe wire. At the same time the body 14.- is given its proper lateralsize and sh ape,- and since slight variations in length are immaterial,no further sizing of .the brush is necessary. The

lower end of plunger 13 is curved so that the operation of forming thebrush body gives the roper radius curve to the contact end of the brush.

In case the wire 12 is made of deoxidized copper or other specialmaterial, the brush may now be passed through the usual baking process,but in case the pigtail wire is of ordin'ary copper, the old practicedoes not give good results. It is well known that all commercial coppercontains a certain amount of cuprous oxide in solution, and if thiscopper wire, or any copper wire, is heated in an oxidizing atmospherethe copper will become embrittled. If copper wire containing oxide isheated in a reducing atmosphere it is also embrittled. Therefore if thewire used is the ordinary commercial article, in order to maintain itsbrightness and strength, it must be heated in a this purpose I prefer touse steam, as being the cheapest inert atmosphere, also the most readilymaintained. The brushes, as they are ejected from the pill machine, arepassed to a conveyor which carries them through a heat-treating furnacecontaining a suitable atmosphere for any desired'interval.

The brus es may be molded together with their pigtails in a continuouslyoperating machine, and discharged as fast as they are made onto acontinuously moving conveyor (I include intermittent operation withinthe intended meaning of the terms continuously operating andcontinuously moving) the furnace may be tubular, sealed at each end by awater-seal into which the ends of the tube are depressed, and theconveyor may emerge from one water-seal, pass thence through the furnacetube, then down into and through the other water-seal, to a place ofdischarge.

7 A steam or other neutral atmosphere is maintained in the furnace, forinstance, by intro ducing steam at the far end of the tube and allowingit to escape at the inlet end of the tube, that is, the end .where theconveyor enters. The result is that the desired atmosphere ismaintainedin the tube, deleterious ga es, &c. coming from the brushes inthe course of the baking operation being swept out with the ventilatingflow of steam. The furnace tube is heated in any preferred manner, sothat the brushes passing through are subjected to direct radiation ofheat. Consequently the baking is accomplished very quickly, as comparedwith the old process, in which an insulating mass of sand had to beheated before the baking heat reached the brushes by conduction. Mymethod shows another advantage in the fact that it minimizes heatlosses. With the old practice, each batch of brushes, with itssurrounding sand, had to be heated up, heat maintained for a long periodand then cooled; whereas, with my method there is no alternate heatingand cooling. The furnace remains hot. Furtherneutral atmosphere, andfor,

more, I am able to make a test of any individual among the succession ofbrushes coming out of the furnace, whereas with the old method no testis possible until after a whole batch has been completed beyond thepossibility of error-correction.

While such an arrangement would not be essential, I contemplateproviding a furnace tube length and/or conveyor speed properlycoordinated with the output of the moldin machine, so that asubstantially continuous manufacturing process may be had.

It will be understood that the heat maintained in the furnace will befrom 650 to 750 C., or whatever temperature may be best for theproduction of a brush with desired durable mechanical and electricalqualities, and with the adjacent surfaces of pigtail and brush properlyalloyed, fused, merged or cemented together.

After the brush is discharged from the furnace the clip 16 is attachedto the ends of the pigtail wire in any preferred manner, and the brushis ready for use without any further operations.

In ordinary practice the electrical contact between the pigtail and thebrush body presents a very serious problem. Even if the contact isfairly satisfactory when the brush is new, on standing for a period oftime oxidizing of the surfaces in contact may take place and theresistance of the contact may increase several hundred or even severalthousand per cent. Various means have been resorted to to make pigtailcontact electrically permanent, as by the use of mercury or itscompounds to produce amalgamation; but trouble has arisen even underthese conditions. With my method the pigtail joint is as electricallypermanent as the brush itself. This result is obtained because thepowdered copper is forced into all the confronting interstices of thewire during the pressing operation, and during the 'bakin there is anactual cementation or fusion of t e powder and the copper comprising thepigtail; or, to put it in another way, there is a mer ing of thesurfaces of pigtail and surrounding brush.

The process disclosed reduces the amount of material as well as laborrequired to produce the finished article, and produces a superiorcommutator brush inexpensively.

I claim 1. The process of producing a commutator brush which comprisesthe steps of holding the intermediate portion of an uncoated wire inspaced relation to the die block of a pill machine, pressing suitablepowdered material about the wire to form a body having the width andthickness of the finished brush, and subjecting the article to a bakingoperation in a non-injurious atmosphere.

2. The process of producing a commutator brush which comprises the stepsof holding an uneoated wire in spaced relation to the die block of a.pill machine, pressing suitable powdered material about the wire to forma body having the width and thickness of the finished brush, andsubjecting the article to a baking operation in a neutral atmosphere tocause alloying between the wire and the powdered material.

3. The process of producing a commutator brush which comprises placingthe intermediate part of a piece of wire into a mold having lateraldimensions corresponding to the lateral dimensions of the finishedbrush, placing a charge of powdered material in the mold, andcompressing the charge from a side corresponding to an end of thefinished brush.

4. The process of producing a commutator brush which comprises placingpart of a conducting wire in a mold having the lateral dimensions of thefinished brush, placing a charge of powdered material in the mold, andbrush which comprises placing part of a conresponding to an end of thefinished brush, thereby simultaneously compressing the powdered materialinto a cohesive mass surrounding part of the conducting wire and moldingthe powdered material into a body having the lateral dimensions of thefinished brush.

In testimony whereof I aflix my si ature.

EVERETT J. L.

